Comprehensive pulping system for producing paper pulp



y 1956 A. P. SCHNYDER 3,259,538

COMPREHENSIVE PULPING SYSTEM FOR PRODUCING PAPER PULP 5 Sheets-Sheet 1 9a 9 Q u.

O (I) (D N (D 3 s E r-- qo P INVENTOR Q AUXILIUS P. SCHNYDER BY frizflgezzsa@et/ ATTORNEY July 5, 1966 A. P. SCHNYDER 3,259,533

COMPREHENSIVE PULPING SYSTEM FOR PRODUCING PAPER PULP Filed April 22,1963 5 Sheets-Sheet 2 INVENTOR AUXILIUS P. SCHNYDER July 5, 1966 A. P.SCHNYDER COMPREHENSIVE PULPING SYSTEM FOR PRODUCING PAPER PULP 5Sheets-Sheet 5 Filed April 22, 1963 N OE INVENTOR AUXILI us P. SCHNYDERBY W ATTORNEY United States Patent 3,259,538 COMPREHENSIVE PULPINGSYSTEM FOR PRUDUCENG PAPER PULP Auxilius P. chnyder, Bogota, N..I.,assignor to The Lummus Company, New York, N.Y., a corporation ofDelaware Filed Apr. 22, 1963, Ser. No. 274,419 12 Claims. (Cl. 162-19)This present invention relates to an improved method and apparatus forthe delignification of cellulosic materials to prepare cellulosic fibersand, more particularly,

to a comprehensive, continuous system for treating cellulosic materialwhich extends from a raw chip supply source through discharge of thewashed pulp for final processing.

In accordance with a preferred embodiment of the present invention, thechips are initially deaerated in a feed tank maintained under vacuum andsubmerged in liquor therein to form a slurry of suitable consistency.The slurry is then pumped to an i-mpregnator where the chips areimpregnated with cooking liquor by being subjected to successive,incrementally increasing hydraulic pressures. From the impregnator, thechip slurry is passed to a digester, and excess liquor is recycled tothe feed tank. After digestion, the chips are washed within thedigester. A high temperature liquor of high solids concentration isseparated from the pulp in the initial washing within the digester. Thepulp is discharged into a blow tank provided with means to enableimproved heat recovery and condensing of flash steam within the blowtank. The pulp is then further washed in vacuum type washers. A portionof the steam flashed in the blow tank is passed to the headers of thevacuum type washers to minimize air infiltration and foaming. The wasteliquor is sent to conventional multiple-effect evaporators forconcentration prior to smelting.

A primary object of the present invention is to provide an improvedcomprehensive pulping system.

Another object of the present invention is to provide an improvedcontinuous process for delignifying cellulosic material to pulp of highquality and yield.

Another object of the present invention is to provide an improvedcontinuous process for delignifying cellulosic material including .amethod of washing digested pulp within a continuous digester.

Still another object of the present invention is to provide an improvedcontinuous process for delignifying cellulosic material includingimproved tank discharge means for submerging cellulosic material withincooking liquor to form a slurry of suitable pumping consistency.

A further object of the present invention is to provide an improvedcontinuous process for delignifying cellulosic material including acontinuous digester of novel structure enabling .an initial washingoperation to be carried out within the digester.

A still further object of the present invention is to provide animproved continuous process for delignifying cellulosic materialincluding means to recover heat from the pulp and liquor leaving thedigester.

These and other objects, features and advantages of the presentinvention will become more apparent from the following description takenin conjunction with accompanying drawings wherein:

FIGURES la and 1b together show a schematic flow diagram illustratingone embodiment of the comprehensive pulping system;

FIGURE 2 is a vertical sectional view through a portion of the vacuumtank and chip submergence means of FIGURE 1a;

FIGURE 3 is a horizontal cross sectional view on the line 33 of FIGUREla through the washing zone; and

FIGURE 4 is an enlarged cross-sectional view of a drainage member of thewasher taken along the lines 4-4 of FIGURE 3.

Referring now to the drawings, and more particularly to FIGURE la, woodchips or like cellulosic material are passed from a main chip siloincluding a vibration hammer 12 into a vibrating feeder device 14 'orother suitable chip metering device and introduced into a vacuum tank16. Liquor in line 18, comprised of a solution of fresh cooking liquorand recirculated liquor, is introduced into tank 16 as will be explainedmore fully hereinafter. Suitable liquid level control means (not shown)may be provided to maintain the liquor level in tank 16 within thedesired range so that only .a portion of the body of chips within tan-k16 is below the level of the liquor. Air is withdrawn from the tank 16through vacuum line 20 and pump '22. The chips, after being subjected tothe vacuum, are gradually submerged beneath the level of the cookingliquor within tank 16. This gradual submergence is also effective todisplace air from the pores of the chips.

The slurry discharge mechanism of tank 16 is best shown in FIGURE 2. Anannular housing 24 is rigidly secured to a flange 26 of the side walls28 of vessel 16. Suitable support means 29 are welded or otherwisefastened to side walls 28 above housing 24. Housing 24 is also rigidlysecured to the bottom wall 30 of tank 16. A hollow chip deflectingmember 32 having an essentially conic-a1 upper surface projects upwardlythrough the center of bottom wall 30. Member 32 is provided with opposedopenings 34 and with a gear housing 36 mounted interiorly thereof bysuitable support elements 38. Casing 40 is rotatably positioned Withinhousing 24 by means of an annular gear ring 42 driven by gear 44, ashaft 46 extending through bottom wall 30, and a motor 48.

Opposed screw conveyors 50 are mounted above and adjacent to theslightly tapering inner surface of bottom Wall 30. Screw conveyors 50extend at their outer ends through apertures in casing 40 and aresecured to roller members 52 which support the lower end of casing 40above the upper surface of bottom wall 30. At their inner ends, screwconveyors 50 are secured to bevel gears 54 within gear housing 36. Amotor 56 having a drive shaft 58 extending through suitable bearingmeans into housing 36 is provided with a drive gear 60 engaging gears 54for rotating screw conveyors 50. Screw conveyors 50 are provided withscrew threads of progressively increasing height to facilitate movementof the slurry through apertures 34 land into a discharge conduit 62. Inaddition to rotation about their own axes, the screw conveyors 50 slowlyrotate about the axis of vessel \16 by means of mot-or 48 and gears 42and 44, so that the entire bottom of vessel 16 is swept by conveyors 50to prevent stagnation of the chips within vessel 16.

Referring to FIG-UR'E la, the slurry in conduit 62 is passed to transferpump 64 and is pumped through the line 66 to an irnpregnator, generallydesignated by reference numeral 68, which is preferably of the typeshown in my copending application entitled Pressure Impregnation DeviceS.'N. 274,422 filed April 22, 1963 now Patent No. 3,215,591, which isincorporated herein by reference. A bypass line is connected from pump64 to liquor line 18.

As set forth more fully in my copending application,

the impregnator 68 consists of a stationary outer casing and an innerrevolving barrel assembly including a plurality of open ended tubularmembers constituting chip receiving passageways. Impregnator-68 is shownin a developed view of FIGURE la to better illustrate its function. Theslurry in line 66 i introduced through an inlet port 72 in thestationary casing into a tubular member present at the inlet station. Acorresponding port 74 in the top of the stationary outer casing isprovided with a screen to prevent chip passage therethrough whileallowing excess liquor to be recycled in line 76 to liquor supply line18. During the residence period of a tubular member in alignment withports 72 and 74, the member will be filled with chips.

The rotor assembly is then cyclically rotated to bring a tubular memberfilled only with liquor to the inlet station and to move the chip-filledtubular member into alignment with port 78. Port 78 is supplied with ahigher pressure liquor through line 80 by pump 82, and line 81 leadingfrom liquor supply line 18. Similarly, the chips are subjected tosuccessively increasing hydraulic impregnating pressure when inalignment with ports 84 and 86 which are supplied with high pressureliquor through lines 88 and 90, respectively, by pump 92 connected toliquor supply line 18 by line 91. Upon the next cyclical rotation of therotor assembly, the filled tubular member is moved to a dischargestation in alignment with the ports 94 and 96. Port 94 is supplied withliquor through line 98 to flush chips out of the tubular member throughdischarge port 96 into line 100 as a chipliquor slurry. During passagethrough impregnator 68, the chips are uniformly impregnated bysubjecting the chips to a high hydraulic pressure several times that ofthe standard cooking pressure. Additionally, by limiting the volume ofchips subjected to successively higher hydraulic pressure stages with afinal pressure in the order of 600 p.s. i.g., rapid impregnation of thechip may be effected.

The slurry in line 100 is introduced into a chip drainage device 102 ofknown construction including a tapering, perforated internal screenmember containing a screw conveyor. Liquor in excess of that requiredfor digestion is passed through the screen member and is recycledthrough line 104, pump 106 and heat exchanger 108 to line 98 and port 94of the impregnator 68. This external heating cycle is described morefully in my aforementioned copending application.

The chips are now passed from strainer 102 through line 110 into adigester 112 corresponding in size and hape to a standard digester. Thedigester 112 is provided with a conventional access manhole 128 and ventline 122. Steam at a pressure of p.s.i.g. is introduced into thedigester 112 through steam line 124 to elfect digestion of the chips innon-submergence. The chips may be digested while submerged in cookingliquor by supplying the entire heating requirements by the recycledliquor passing through heat exchanger 108. A combination of steam andheated cooking liquor is also contemplated to supply the heatingrequirements for effecting delignification of the cellulosic material.

The chips are delignified to pulp during passage downwardly through thedigester 112, and the residence time is regulated by suitable controlmeans (not shown) to insure substantially complete digestion. Recycledliquor in line 126, as more fully hereinafter described, is introducedinto the digested pulp in the lower portion of digester 112 to dilutethe suspension to a consistency of from about 1% to about 3%. The pulpis passed through a conduit 116 to a washer 118. A suitable agitator 128may be provided in conduit 116 to insure good pulp dispersion within thechip liquor suspension.

The suspension is passed upwardly through washer 118 which. includes aplurality of perforated liquor drainage members 130. Drainage members130 preferably extend in a saw-tooth offset fashion transversely fromone side to the other of an internal perforated drainage cylinder 132provided within Washer 118. The drainage cylinder .132 is incommunication with the ends of drain age members 130. Drainage members130 preferably consist of support pipes secured to the walls of drainagecylinder 132 which support a mesh or other similar perforated wallportions. The apexes of members 130 are preferably imperforated V-shapedtroughs and serve as drain troughs which discharge the liquor intoperforated cylinder 132. Liquor is removed from the dilute suspensionthrough members 130 and cylinder 132. In FIG- URE 4, a drainage member130 is illustrated having perforations 131 along the side walls andhaving an imperforated V-shaped trough 133. The consistency of the pulpis increased to about 10% to about 12% at the top of washer 118 wherethe pulp is skimmed off by a scraper 134 and passed via line 135 into alaunder 136.

The liquor removed by means of members 130 and cylinder 132 isintroduced into a spent liquor tank 138 through line 140 at atemperature below the cooking temperature, for example, between about250 F. to about 300 F. with a high concentration of dissolved solids. Aportion of the liquor in tank 138 is pa sed through line 142 by pump 144to be introduced through line 126 into digester leg portion 114. Theremainder of the spent liquor is passed through line 146 tomultiple-effect evapor-ators (not shown) for concentration andsubsequent smelting, as is conventional in the art. However, since theliquor is recovered at a higher temperature than in prior artinstallations, an improved overall heat recovery is achieved. Steamliberated in tank 138 is vented through line 148 to heat exchanger 150to preheat makeup cooking liquor in line 18.

The pulp in launder 136 is passed through blow line 152 provided with ablow valve 154 into a small cyclone 156 at the inlet to a blow tank 158.Cyclone 156 distributes the stock in a thin sheet for tangentialdischarge through line 160 into blow tank 158 to facilitate theliberation of steam from the stock with minimum fibre entrainment.

Flash steam is liberated from the blown stock and is passed upwardlyinto a comically-shaped funnel 162 wherein the steam is condensed bycontact with cooling water introduced through line 164 and discharged inspray form through a perforated plate 166. Steam condensate and coolingwater is removed from the funnel 162 through line 167 and is passed intoan accumulator tank 168. Blow tank 158 also receives condensate from theheat exchanger 150 through line 170. Blow tank 158 additionallyfunctions as a stock storage vessel balancing digester operations withfinal washing operations in vacuum washers 172 and 174.

Accumulator 168 is provided with an external liquor circuit includingline 180, heat eychanger 182, lines 184, 186, 188 and pump 190. Atemperature responsive flow control valve 192 is provided in bypass line186 to regulate the flow of water to heat exchanger 182 through line180, and the temperature of incoming fresh water supplied to heatexchanger 182 through line 194. From heat exchanger 182, the fresh wateris passed through line 196 to a heat exchanger 198 in vent line 178. Theheated water is passed through line 200 to a hot water storage tank 202from which water is removed to process as desired through line 204 bypump 206. A portion of the incoming fresh Water in line 194 may beintroduced dirlecly into the accumulator 168 through lines 208 and Fromaccumulator 168, water is passed through line 210 by pump 212 to line164 and perforated plate 166 for condensing flash steam as previouslydescribed. Water is also withdrawn from accumulator 168 through line 214by pump 216 and is passed through line 218 to vacuum washer 174 as willbe discussed hereinafter.

Pulp diluted to a suitable consistency in blow tank 158 is withdrawnthrough line 230 and is passed through line 232 to a pressurized pulpscreen assembly 234. Screen assembly 234 further refines the stock andreturns oversized fibre masses to blow tank 158 through line 236. Thestock from screen assembly 234 is passed through line 238 to an inletbox 240 adjacent vacuum washer 172. The stock is taken up on aconventional perforated drum 242 and sprayed with :a wash medium fromspray head 244. The wash medium is supplied to spray head 244 from thethird stage vacuum washer 174 through line 246. Liquor and wash mediumdrain through perforated drum 242 and are removed by line 248 to awasher liquor seal tank 250 which is provided with a baflie 252 and avent line 254. A portion of the liquor in tank 250 is removed throughline 256 and passed by pump 258 through lines 260 and 126 to digester112. The remainder of the liquor in tank 250 is passed through line 262by pump 264 and is passed through line 266 to blow tank 158 to dilutethe stock therein, or through line 268 for admixture with the dilutedpulp in line 230 being introduced into the screen assembly 234 throughline 232.

The pulp stock from vacuum washer 172 is discharged into a trough 27 0for treatment to break up sheeted pulp. The pulp is diluted in trough270 with liquor supplied from a liquor seal tank 272 through line 274,pump 276, and lines 278 and 280. The diluted pulp in trough 270 is actedupon by blades 282 and is passed to the rotating perforated drum 284 ofvacuum washer 174. Here the pulp is washed by water supplied to a sprayhead 286 through line 218 from accumulator 168. The wash water passesthrough the perforations of drum 284 and is removed by line 288 to theliquor seal tank 272 provided with suitable baflles 290 and a vent 292.The pulp which has now undergone a three-stage washing is dischargedfrom cylinder 284 into hopper 294 for further processing.

Spray heads 244 and 286 of vacuum Washers 172 and 174, respectively, areenclosed within housings 296 and 298, respectively. Housings 296 and 298are supplied with flash steam from blow tank 158 through line 300 undercontrol of valve 302 to essentially prevent foaming at vacuum washers172 and 174 and their sea-l tanks 250 and 272 by eliminating airinfiltration.

While I have shown and described several embodiments in accordance withthe present invention, it is understood that the same is not limitedthereto, but is susceptible of many changes and modifications within thespirit and scope thereof, and I, therefore, do not Wish to be limited tothe details shown and described herein, but intend to cover all suchchanges and modifications as are encompassed by the scope of theappended claims.

I claim:

1. A process for digesting cellulosic material comprising vacuumdeaerating said material, submerging said material in liquor forming aslurry of pumpable consistency, impregnating said material by subjectingthe material to progressively increasing hydraulic pressures,introducing the impregnated material into a digester, digesting saidimpregnated material to pulp in non-submergence in the presence ofsteam, diluting the pulp within the digester with additional liquor,transferring the diluted pulp to a Washer, washing the diluted pulp insaid Washer, removing liquor from the diluted pulp substantially at thecooking temperature, introducing the washed pulp a a thin stream into ablow tank, condensing the steam within the blow tank by direct contactwith cooling water, passing the steam condensate and cooling Water to anaccumulator tank, vacuum washing the pulp removed from said blow tank ina vacuum washer having a wash liquid sprayer, returning liquor from thevacuum washing step to said blow tank, and injecting steam from saidblow tank into a header surrounding the wash liquid sprayer of thevacuum washer.

2. A process for digesting cellulosic material comprising vacuumdeaerating said material, submerging said material in liquor forming aslurry of pumpable consistency, impregnating said material by subjectingthe material to progressively increasing hydraulic pressures,introducing the impregnated material into a digester, continuouslydigesting said impregnated material to pulp in said digester, dilutingthe pulp within said digester, removing liquor from the pulpsubstantially at the cooking temperature,

introducing the pulp into a blow tank, condensing the steam Within saidblow tank by direct contact with cooling water, passing the steamcondensate and cooling water to an accumulator tank, vacuum washing thepulp removed from said blow tank in a vacuum washer having a wash liquidsprayer, returning liquor from the vacuum washing step to said blowtank, and injecting steam from said blow tank into a region surroundingthe wash liquid sprayer of the vacuum washer.

3. In a process for digesting cellulosic material comprising deaeratingsaid material, impregnating said material, introducing said materialinto a digester, digesting, said material to pulp, introducing the pulpinto a blow tank, vacuum washing the pulp removed from said blow tank ina vacuum Washer having a wash liquid sprayer, the improvement whichcomprises returning liquor from the vacuum washing step to said blowtank, and injecting steam formed in said blow tank into a headersurrounding the wash liquid sprayer.

4. A process for digesting cellulosic material comprising deaeratingsaid material, impregnating said material, introducing said materialinto a digester, digesting said material to pulp, diluting the pulpwithin the digester with additional liquor, transferring the dilutedpulp to a Washer, washing the diluted pulp in said washer, removingliquor from the diluted pulp, introducing the washed pulp into a blowtank, vacuum washing the pulp removed from said blow tank in a pluralityof vacuum washers, each having a wash liquid sprayer, returning liquorfrom the vacuum washing step to said blow tank, and injecting steamformed in said blow tank into headers surrounding the wash liquidsprayers.

5. Apparatus for treating wood chips or the like, comprising asubstantially upright tank, an annular housing rigidly secured to thebottom of said tank and closed off by a bottom wall, a hollow chipdeflecting member having an essentially conical upper surface projectingabove said bottom wall substantially in the center thereof, saiddeflecting member being provided with openings into the interiorthereof, gear means mounted within the interior of said deflectingmember, a casing rotatably positioned within said housing, drive gearmeans for rotating said casing, and a plurality of screw conveyorsmounted at the outer ends thereof upon said casing and at the other endsthereof being adapted to convey chips through said openings into theinterior of said deflecting member.

6. Apparatus for treating wood chips or the like, comprising asubstantially upright tank, an annular housing rigidly secured to thebottom of said tank and closed off by a bottom wall, a hollow chipdeflecting member having an essentially conical upper surface projectingabove said bottom wall substantially in the center thereof, saiddeflecting member being provided with opposed openings to the interiorthereof, gear means mounted within the interior of said deflectingmember, a casing rotatably positioned within said housing and providedwith an annular gear ring, drive gear means cooperating with said gearring, a plurality of screw conveyors mounted adjacent to the uppersurface of said bottom wall with their outer ends mounted upon saidcasing and with their inner ends extending through said openings in saiddeflecting member, means to rotate said screw conveyors to convey chipsthrough said openings into the interior of said deflecting member, and adischarge conduit in communication with the interior of said deflectingmember.

7. Apparatus for pulping cellulosic material which comprises: tank meansto submerge said cellulosic material in cooking liquor to form a slurryof said cellulosic material and said liquor; a first conduit means; animpregnator for receiving said slurry in fluid communication with saidtank means through said first conduit means, said impregnator includingmeans to progressively increase the hydraulic pressure of said slurry; adigester; a liquor supply means for diluting said pulp leaving saiddigester; a second conduit means; a washer in fluid communication withsaid digester through said second conduit means for receiving dilutedpulp, said washer having a plurality of perforated drainage membersextending trans versely across said washer in a saw-toothed arrangement;and a third conduit means for withdrawing liquor out of said washer fromsaid drainage members.

8. Apparatus for pulping cellulosic material which comprises: tank meansto submerge said cellulosic material in cooking liquor to form a slurryof said cellulosic material and said liquor; a first conduit means; animpregnat-or for receiving said slurry in fluid communication with saidtank means through said first conduit means, said impregnator includingmeans to progressively in crease the hydraulic pressure of said slurry;a digester; a liquor supply means for diluting said pulp leaving saiddigester; a second conduit means; a washer in fluid communication withsaid digester through said second conduit means for receiving dilutedpulp, said washer having a plurality of perforated drainage membersextending transversely across said washer in a saw-toothed arrangement;and a third conduit means for withdrawing liquor out of said washer fromsaid drainage members; a fourth conduit means; a blow tank for receivingdischarge pulp from said washer through said fourth conduit means; andcondensing means including cooling water spray means within said blowtank to condense steam flashed by entry of the pulp into said blow tank.

9. An apparatus for digesting cellulosic material which comprises: adigester; means to supply cellulosic material and cooking liquor intosaid digester; means to introduce liquor into a lower region of saiddigester to dilute digested pulp; conduit means; a washer in fluidcommunication with said digester through said conduit means forreceiving diluted pulp, said washer including a p1u rality of drainagemembers spaced in a staggered arrangement, each drainage memberincluding essentially V- shaped imperforated bottom portions andperforated side wall portions, said imperforated bottom portionsconstituting drainage troughs for liquor passing through the side wallportion; and means to remove washed pulp from the top of said washer.

10. An apparatus for digesting cellulosic material which comprises: adigester; means to supply cellulosic material and cooking liquor intosaid digester; means to introduce liquor into the lower portion of saiddigester to dilute digested pulp; conduit means, a washer in fluidcommunication with said digester through said conduit means forreceiving diluted pulp, said washer including a plurality of drainagemembers spaced in staggered arrangement, each drainage member includingessentially V- shaped imperforated bottom portions and perforated sidewall portions, said imperforated bottom portions constituting drainagetroughs for liquor passing through said side wall portions, an annularperforated drainage cylinder within said washer in fluid communicationwith 8 the drainage troughs of said drainage members; and means toremove wash pulp from the top of said washer.

11. An apparatus for digesting cellulosic material which comprises: adigester; means to supply cellulosic material and cooking liquor intosaid.digester, means to supply steam into said digester to effectdelignification of the cellulosic material; means to introduce liquorinto the lower portion of said digester to dilute delignified pulp;conduit means; a washer in fluid communication with said digesterthrough said conduit means for receiving diluted pulp, said washerincluding a plurality of drainage members spaced in a staggeredarrangement, each drainage member including essentially V-shapedimperforated bottom portions and perforated side wall portions, saidimperforated bottom portions constituting drainage troughs for liquorpassing through said side wall portions; and means to remove wash pulpfrom the upper portion of said washer.

12. An apparatus for delignifying cellulosic material which comprises: adigester; means to supply cellulosic material and cooking liquor intosaid digester; means to supply steam to said digester to effectdelignification of the cellulosic material; means to introduce liquorinto a lower portion of said digester to dilute the delignified pulp;conduit means; a washer in fluid communication with said digesterthrough said conduit means to receive diluted pulp, said washerincluding a plurality of drainage members spaced in a staggeredarrangement, each drainage member including essentially V-shapedimperforated bottom portions and perforated side wall portions, saidimperforated portions constituting drainage troughs for liquor passingthrough the side wall portions; an annular perforated drainage cylinderpositioned within said washer in fluid communication with the drainagetrough of said drainage members; and means to remove washed pulp fromthe upper portion of said Washer.

References Cited by the Examiner UNITED TATES PATENTS 2,969,156 1/1961Miller et a1. 214-1782 2,999,784 9/1961 Hullman 162-19 3,050,201 8/1962Humphrey 214-17.82 3,061,007 10/1962 Rich 162-237 3,081,820 3/ 1963Schnyder 162-246 3,085,624 4/1963 Horstman 162-237 3,165,436 1/1965Bennett et a1. 162-19 FOREIGN PATENTS 175,783 8/1953 Austria.

852,892 11/1939 France. 1,078,667 5/1954 France.

DONALL H. SYLVESTER, Primary Examiner.

J. H. NEWSOME, Assistant Examiner.

1. A PROCESS FOR DIGESTING CELLULOSIC MATERIAL COMPRISING VACUUM DEAERATING SAID MATERIL, SUBMEGING SAID MATERIAL IN LIQUOR FORMING A SLURRY OF PUMPABLE CONSISTENCY IMPREGNATING SAID MATERIAL BY SUBJECTING THE MATERIAL TO PROGRESSIVELY INCREASING HYDRAULIC PRESSURES, INTRODUCING THE IMPREGNATED MATERIAL INTO A DIGESTER, DIGESTING SAID IMPREGNATED MATERIAL TO PULP IN NON-SUBMERGENCE IN THE PRESENCE OF STEAM, DURING THE PULP WITHIN THE DIGESTER WITH ADITIONAL LIQUOR, TRANSFERRING THE DILUTED PULP TO A WASHER, WASHING THE DILUTED PULP IN AAID WASHER, REMOVING LIQUOR FROM THE DILUTED PULP SUBSTANTIALLY AT THE COOKING TEMPERATURE, INTRODUCING THE WASHED PULP AS A THIN STREAM INTO A BLOW TANK, CONDENSING THE STREAM WITH IN THE BLOW TANK B DIRECT CONTACT WITH COOLING WATER, PASSING THE STREAM CONDENSED AND COOLING WATER TO AN ACCUMULATOR TANK, VACUUM WASHING THE PULP REMOVED FROM SAID BLOW TANK, IN A VACUUM WASHER HAVING A WASH LIQUID SPRAYER,RETURNING LIQUOR FROM THE VACUUM WASHING STEP TO SAID BLOW TANK, AND INJECTING STREAM FROM SAID LIQUID SPRAYER OF THE VACUUM WASHER.
 5. APPARATUS FOR TREATING WOOD CHIPS OR THE LIKE, COMPRISING A SUBSTANTIALLY UPRIGHT TANK, AN ANNULAR HOUSING RIGIDLY SECURED TO THE BOTTOM OF SAID TANK AND CLOSED OFF BY A BOTTOM WALL, A HOLLOW CHIP DEFLECTING MEMBER HAVING AN ESSENTIALLY CONICAL UPPER SURFACE PROJECTING ABOVE SAID BOTTOM WALL SUBSTANTIALLY IN THE CENTER THEREOF, SAID DEFFECTING MEMBER BEING PROVIDED WITH OPENINGS INTO THE INTERIOR THEREOF, GEAR MEANS MOUNTED WITHIN THE INTERIOR OF SAID DEFFECTING MEMBER, A CASING ROTATABLE POSITIONED WITHIN SAID HOUSING, DRIVE GEAR MEANS FOR ROTATING SAID CASING, AND A PLURALITY OF SCREW CONVEYORS MOUNTED AT THE OUTER ENDS THERREOF UPON SAID CASING AND IN THE OTHER ENDS THEREOF BEING ADAPTED TO CONVEY CHIPS THROUGH SAID OPENINGS INTO THE INTERIOR OF SAID DEFFECTING MEMBER. 